Nickel aluminum alloys (nickel aluminides) are corrosion resistant at elevated temperatures. Reaction synthesis can be used to form these alloys from a mixture of fine elemental powders. In this technique, a powder with the desired composition is mixed in a ball mill and then pressed into a die. The pressed powder is then heated to initiate an exothermic reaction that forms nickel aluminide. The resulting material is stronger and lighter than stainless steel. However, the material never becomes fully molten in this processing technique. This traps porosity in the microstructure that can reduce the overall strength of the material. Furthermore, the resulting alloy can retain some of the microstructural features of the pre-reacted form.
Thermal spray processing is the deposition of molten or semi-molten material onto a substrate to create a coating for modifying properties, for dimensional restoration on a part or for producing a three dimensional form. The material being deposited typically comes from a powder, rod or wire feedstock and is heated as it is accelerated towards a substrate by a hot jet of combusting or plasma gas. Upon impact, the molten droplets spread to from splats. A coating or solid object is formed as layer upon layer of these splats deposit on top of already deposited droplets.